1. Field of the Invention
The invention relates to the field of lossless compression/expansion of digital information.
The invention further relates to a transmitting device for transmitting a digital information signal via a transmission medium, including:
a lossy encoder adapted to compress the digital information signal to a lossy encoded signal,
a lossy decoder adapted to expand the lossy encoded signal so as to obtain a replica of the digital information signal,
a first signal combination unit adapted to combine the digital information signal and the replica to a first residue signal,
a lossless encoder adapted to compress the first residue signal to a lossless encoded residue signal, and
a second signal combination unit adapted to combine the lossy encoded signal and the lossless encoded residue signal to a transmission signal for the transmission via the transmission medium.
The invention further relates to a receiving device for receiving a transmission signal, to a method of transmitting a digital information signal via a transmission medium , and to a record carrier obtained by means of the method in accordance with the invention.
2. Description of the Related Art
A transmitting and receiving device of the type defined in the opening paragraphs is known from J. Audio Eng. Soc., Vol. 44, No. 9, pp. 706-719, 1996 September, and the AES preprint 4621 xe2x80x9cRobust Coding of High Quality Audio Signalsxe2x80x9d by Jxc3xcrgen et al, 103rd AES Convention (New York, US). The known transmitting device is intended for efficiently reducing the bit rate of a digital information signal. An encoded signal thus obtained demands less capacity from a transmission medium during transmission. The known receiving device converts the encoded signal into a copy of the original digital information signal.
It is an object of the invention to provide a transmitting and/or receiving device which reduces the bit rate of a digital information signal more efficiently.
To this end, a transmitting device in accordance with the invention is characterized in that the lossless encoder includes: a prediction filter for deriving a prediction signal,
a signal combination unit for combining the prediction signal and the first residue signal so as to obtain a second residue signal, and
an entropy encoder for encoding the second residue signal into the lossless encoded residue signal.
A receiving device in accordance with the invention is characterized in that the lossless decoder includes:
an entropy decoder for decoding the lossless encoded residue signal into a second residue signal,
a signal combination unit for combining the second residue signal and a prediction signal into the first residue signal, and
a prediction filter for processing the second residue signal so as to form the prediction signal.
A method in accordance with the invention is characterized in that the lossless compression includes the following steps:
deriving a prediction signal,
combining the prediction signal and the first residue signal so as to obtain a second residue signal, and
encoding the second residue signal into the lossless encoded residue signal.
The invention is based on the recognition that a prediction filter for an entropy encoder is useful only if the frequency spectrum of the signal applied to the prediction filter has a non-uniform distribution. In the known transmitting device, a digital signal is lossy encoded and lossy decoded to a lossy signal. A residue signal is obtained by combining the digital information signal and the lossy signal. It was expected that when use is made of a suitable algorithm, the frequency spectrum of the residue signal would have a uniform distribution. In such a case, the use of a prediction filter for the entropy encoder would not lead to a bit rate reduction. However, in contradistinction to what was expected, Applicant has been found that the frequency spectrum of the residue signal does not have a uniform distribution. As a result of this, in practice, a prediction filter does contribute to a further reduction of the bit rate.